Electronically controllable brake actuating system

ABSTRACT

The present invention discloses an electronically controllable brake actuating system for automotive vehicles, including an unpressurized pressure fluid supply reservoir, a pressure source actuatable by an electronic control unit, the pressure of which can be applied to wheel brakes of the vehicle, further including a device for detecting the driver&#39;s wish for deceleration as well as valve assemblies inserted upstream of the wheel brakes and connecting the wheel brakes alternatively to the pressure source or the pressure fluid supply reservoir. In order to increase the operational or functional reliability of a system of this type, the present invention discloses the provision of means for detecting gases or air disposed in the system.

RELATED APPLICATION

The present application is a divisional patent application of U.S. Ser.No. 09/601,906 filed on Jan. 29, 2001, now U.S. Pat. No. ______ issued______.

TECHNICAL FIELD

The present invention relates generally to vehicle brakes and moreparticularly relates to an electronically controllable brake actuatingsystem for automotive vehicles.

BACKGROUND OF THE INVENTION

A brake actuating system of this general type is disclosed, for example,in the article ‘Electrohydraulic Brake System—The First Approach toBrake-By-Wire Technology’, SAE Papers 960991. The valve assemblies ofthe prior art brake actuating system which are connected upstream of thewheel brakes are configured as two-way/two-position directional controlvalves in slide-type construction and arranged in pairs, with the inletvalve inserted into the connection between the pressure source and thewheel brakes fulfilling a pressure-limiting function in its first switchposition and releasing the connection in its second switch position. Theoutlet valve that is inserted into the connection between the wheelbrakes and the pressure fluid supply reservoir is configured as anormally closed valve which closes the connection in its first switchposition and opens it in its second switch position.

The above-mentioned publication, however, does not indicate anyprovisions which could eliminate or at least greatly reduce malfunctionswhich are caused in the prior art brake system, e.g. by gas bubbles orair bubbles.

Therefore, an object of the present invention is to improve upon anelectronically controllable brake actuating system of the initiallymentioned type to such effect as to greatly enhance the reliability inoperation and functioning.

According to the present invention, this object is achieved by theprovision of means for detecting gases or air disposed in the system.

To render the idea of the present invention more precise, the means isprovided by a hydraulic arrangement which permits applying a definedpressure fluid volume to at least one wheel brake, with a pressuresensor being arranged for sensing the pressure rise which is caused inthe wheel brake by the effect of the pressure fluid volume. Monitoringis thereby achieved with each actuation.

In an especially favorable improvement of the brake actuating system ofthe present invention, the arrangement is configured as apiston-and-cylinder unit which is interposed between the pressure sourceand the associated wheel brake, and a valve assembly is provided in aline that leads from the pressure source to the piston-and-cylinder unitand permits closing of the line.

Preferably, a line communicating with the pressure fluid supplyreservoir and accommodating a restrictor is interposed between the valveassembly and the piston-and-cylinder unit.

In another favorable embodiment of the present invention wherein thepressure source includes a hydraulic accumulator with a movable mediaseparating element, the hydraulic arrangement is provided by theaccumulator, and there is provision of a travel sensor device forsensing the travel of the movable media separating element, the outputsignal of which corresponds to the defined pressure fluid volume.

In still another favorable embodiment of the subject matter of thepresent invention, the pressure source is arranged in a reservoir filledwith pressure fluid and the accumulator housing has bores which permitthe delivery of the pressure fluid into an unpressurized chamber that isdefined in the accumulator housing by the movable media separatingelement.

To detect damage of the above-mentioned accumulator whose mediaseparating element separates a chamber filled with a pressure fluidunder high hydraulic pressure from a chamber filled with gas, afavorable aspect of the present invention arranges for the mediaseparating element to be configured as a metal diaphragm and thepressure that prevails in the chamber filled with pressure fluid to besignificantly higher than the gas pressure. The difference in pressureis preferably caused by the preload of the metal diaphragm or theadditional force of a spring which acts upon the metal diaphragm. It isensured by the mentioned provisions that in the event of leakage of themetal diaphragm an exchange of media will take place only from thepressure fluid side to the gas side.

In another favorable aspect of the object of the present invention,another possibility of sensing the leaky condition includes that themetal diaphragm has a double wall design and that a media sensor isfitted in the area between both walls which responds to pressure fluidand to gas.

The present invention will be explained in detail in the followingdescription by way of two embodiments making reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a first design of the brake actuatingsystem of the present invention.

FIG. 2 is a circuit diagram of a second design of the brake system ofthe present invention.

FIG. 3 is a design of a pressure source which can be used in the brakeactuating system according to FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electronically controllable brake actuating system of the presentinvention, as shown in the drawings, is comprised of a dual-circuitmaster brake cylinder or tandem master cylinder 2 which is operable bymeans of an actuating pedal 1, cooperates with a pedal travel simulator,and includes two pressure chambers separated from each other andconnected to an unpressurized pressure fluid supply reservoir 3.Connected to the first pressure chamber (primary pressure chamber) byway of a closable first hydraulic line 11 is a wheel brake 7 associatedwith the front axle and a wheel brake 8 associated with the rear axle,for example. Line 11 is shut off by means of a first separating valve12, while in the line portion 17 that leads to the wheel brake 8 anelectromagnetically operable, preferably normally open (NO) pressurecompensating valve 16 is inserted which permits braking pressure controlindividually per wheel, if necessary.

The second pressure chamber of the master brake cylinder 2 to which apressure sensor 13 can be connected is connectable to the other wheelbrake pair 9, 10 by way of a second hydraulic line 14 that can be closedby means of a second separating valve 15. In turn, anelectromagnetically operable, preferably normally open (NO) pressurecompensating valve 19 is inserted into the line portion 18 leading tothe wheel brake 10. Because the design of the hydraulic circuitconnected to the second pressure chamber of the master brake cylinder 2is identical to the brake circuit 11 that has been describedhereinabove, there is no need for further explanations in the followingtext.

As can be seen in the drawings, a motor-and-pump assembly 20 used as anauxiliary-pressure source is provided with a high-pressure accumulator21 which, in turn, includes a pump 23 driven by an electric motor 22 anda pressure-limiting valve 24 connected in parallel to the pump 23. Thesuction side of the pump 23 is connected to the above-mentioned pressurefluid supply reservoir 3 by way of a non-return valve that is notreferred to in detail, while the hydraulic pressure generated by thepump 23 is monitored by a pressure sensor 25.

A third hydraulic line 26 connects the pressure side of the pump 23 orthe high-pressure accumulator 21 to first inlet ports of twoelectromagnetically operable three-way/three-position slide valves 27,28 which are connected upstream of the wheel brakes 7 and 8. Connectedto second inlet ports of the slide valves 27, 28 is one hydraulic line29, 30 respectively, being in connection to the unpressurized pressurefluid supply reservoir 3, on the other hand. Inserted into the line 26that leads to the three-way/three-position slide valve 27, 28 is a firston-off seat valve 31 which is preferably configured as a normally closed(NC) electromagnetically operable two-way/two-position directionalcontrol valve. Connected in line 29 or 30 leading to the pressure fluidsupply reservoir 3 is a second on-off seat valve 32, the design of whichcorresponds to that of the first valve 31. Connected to the outlet portof the three-way/three-position directional control valve 27, 28 is theabove-mentioned line 11 or 17 that leads to the wheel brake 7 or 8 aswell as each one pressure sensor 51, 52 with the aid of which thehydraulic pressure is determined that prevails in the wheel brake 7, 8.

The joint actuation of the motor-and-pump assembly 20 and theelectromagnetic valves 12, 15, 16, 19, 27, 28, 31, 32 is performed by anelectronic control unit 38 to which are sent, as input signals, theoutput signals of an actuating travel sensor 36 that cooperates with theactuating pedal 1 and those signals of the above-mentioned pressuresensor 13, and which permit detecting the driver's wish fordeceleration. However, other means, such as a force sensor sensing theactuating force at the actuating pedal 1, can also be used for thedetection of the driver's wish for deceleration. The output signals ofthe pressure sensors 25, 51 and 52 and the output signals of wheelsensors (shown only schematically) corresponding to the speed of thevehicle are sent to the electronic control unit 38 as further inputquantities, with the wheel sensors associated with the wheel brakes 7, 8being designated by reference numerals 53, 54.

To permit detecting air that might be in the system, there is provisionof a hydraulic arrangement or a piston-and-cylinder unit 33 which isconnected to the above-mentioned hydraulic line 26 downstream of theon-off seat valve 31, on the one hand, and to the line 18 that leads tothe wheel brake 9, on the other hand. The line portion 34 between theline 26 and the piston-and-cylinder unit 33 is closable by means of apreferably normally closed (NC) third on-off seat valve 35. Another line36 in which a restrictor 37 is inserted is connected to the line portionthat leads from the third on-off seat valve 35 to thepiston-and-cylinder unit 33, on the one hand, and to the line that leadsfrom the pressure fluid supply reservoir 3 to the motor-and-pumpassembly 20, on the other hand.

Due to the change-over of the on-off seat valves 31 and 35 on command ofcontrol signals of the control unit 38, the piston of thepiston-and-cylinder unit 33, which is not referred to in detail, isacted upon by the pressure that prevails in the high-pressureaccumulator 21 and displaces by its movement a defined pressure fluidvolume into the wheel brakes 9, 10. The pressure sensors 49, 50connected to the wheel brakes 9, 10 determine a pressure valueresponsive to the pressure fluid volume. In case the pressure valuedetermined does not correspond to a previously fixed relationshipbetween volume and pressure, air or gas prevails in the system. Thismust be signaled for safety reasons.

In the second embodiment shown in FIG. 2, a travel detection device,such as a travel sensor 40, is used to detect the air prevailing in thesystem. Sensor 40 senses the actuating stroke or travel of the mediaseparating element of the high-pressure accumulator mentioned withrespect to FIG. 1. The media separating element (not illustrated) of thehigh-pressure accumulator 39 shown in FIG. 2 is configured as a metaldiaphragm. The above-mentioned pressure fluid volume that is requiredfor the pressure increase in the wheel brakes is derived from the sensedtravel of the metal diaphragm. The information about the pressure fluidvolume is used together with the information about the hydraulicpressure introduced into the wheel brakes for the comparison with thestored volume-pressure characteristic curve.

The hydraulic high-pressure accumulator is configured as a piston-typeaccumulator 41 in the design of the above-mentioned pressure source 20shown in the embodiment of FIG. 3. The pressure source 20 is preferablyarranged in a reservoir 42 filled with pressure fluid. The housing 43 ofthe piston-type accumulator 41 includes supply bores 45 which open intoan unpressurized chamber 46 bounded in the housing 43 by seals 47, 48arranged on the piston 44. Air is thereby prevented from propagatinginto the system by way of seals 47, 48. It is another advantage that theseals 47, 48 are permanently kept in a humid condition, with the resultthat their useful life is considerably prolonged.

1-10. (canceled)
 11. Electronically controllable brake actuating systemfor automotive vehicles, comprising: means for measuring fluid pressureexerted by the brake system fluid, means for measuring volume change ofbrake system fluid, means for detecting the presence of gases disposedin the brake system fluid.
 12. Electronically controllable brakeactuating system as claimed in claim 11, wherein said detecting meansincludes a hydraulic arrangement which displaces a defined pressurefluid volume, a pressure sensor arranged for sensing the pressure risewhich is caused by the volume displacement by the effect of the pressurefluid volume.
 13. Electronically controllable brake actuating system asclaimed in claim 12, wherein the pressure source includes a hydraulicaccumulator with a movable media separating element, and wherein thehydraulic arrangement is provided by the accumulator, and, wherein saidaccumulator further includes a travel sensor device for sensing thetravel of the movable media separating element, the output signal ofwhich corresponds to the defined pressure fluid volume. 14.Electronically controllable brake actuating system as claimed in claim13, wherein the pressure source is arranged in a reservoir filled withpressure fluid, and in that the accumulator housing has bores whichpermit the delivery of the pressure fluid into an unpressurized chamberthat is defined in the accumulator housing by the movable mediaseparating element.
 15. Electronically controllable brake actuatingsystem as claimed in claim 13, wherein the media separating elementseparates a chamber filled with pressure fluid and subjected to highhydraulic pressure from a chamber filled with gas, wherein the mediaseparating element is configured as a metal diaphragm, and in that thepressure that prevails in the chamber filled with pressure fluid issignificantly higher than the gas pressure.
 16. Electronicallycontrollable brake actuating system as claimed in claim 15, wherein thedifference in pressure is caused by the preload of the metal diaphragm.17. Electronically controllable brake actuating system as claimed inclaim 15, wherein the difference in pressure is caused by the additionalforce of a spring which acts upon the metal diaphragm. 18.Electronically controllable brake actuating system as claimed in claim13, wherein the media separating element separates a chamber filled withpressure fluid and subjected to a high hydraulic pressure from a chamberfilled with gas, wherein the media separating element is configured as adouble-wall metal diaphragm, and in that a media sensor is fitted in thearea between the two walls which responds to pressure fluid and to gas.